Process for color cinematography



Patented Aug. 31, 1943 2,328,418 PROCESS FOR COLOR CINEMATOGRAPHY Percy D. Brewster, Holmdel, N. J.

No Drawing. Application October 17, 1940,

. Serial No. 361,619

5 Claims. (01. 95--5) My invention relates to a process for determining the degree of development of color separation motion picture negative film.

Contrast or gamma control of color separation negative motion picture film is especially im-' portant when the color prints are to be made by printing the positive film from these negatives and converting the black and white silver images into a dye mordaunt and treating with dye, such as are described in my United States Patent No. 1,992,169, and patent application Ser. No. 343,747, filed July 3, 1940. In processes of this type the positive contrast is greatly increased by the conversion into color, so fiat positive images full of detail are usually required with the size of the grain clumps held to a minimum.

Negative films of many different scenes are spliced together to form a reel from which the color positive films are printed, developed and colored in one continuous strip, making it impractical to give special treatment to any one scene. Therefore, it is necessary so to control the development of negative films, made under all sorts of light conditions, that a continuous color print, made from many of these negatives, can be processed in long lengths under standard conditions.

The positive film requires development to give sufilcient contrast or gamma to form good blacks in the shadows while keeping the highlights clear in order to produce attractive pictures when projected on the screen. It is equally important that this development should not cause grain clumping which, when converted into color, be-

comes very disagreeable on the screen.

Minor variations in exposure are permissible in printing from different negative scenes to get best results, but negatives should be closely uniform in maximum density in the highlights and minimum density in the shadows to be combined into a color reel with uniformly pleasing results. The present practice is to develop all negative to a fixed gamma and to control the exposure accurately by means of photometers, sometimes using white targets from which photometric readings are carefully made. While fairly satisfactory results are obtained by these means, great photographic skill and considerable time are required, and, at best, many scenes photographed in color by this technique leave considerable to be desired.

One object of my invention is to provide a simple and quick process for controlling developmerit of the density of the highlights of a group of negatives by changes of gamma of their development. Another object is to develop a group of negatives to different gammas, so that each of these negatives may be printed by nearly the same amount of light onto the positive film. A

further object is to reduce the time required in photographing a scene in color. To these and other ends my invention comprises the novel features hereinafter described.

My invention consists in first determining a standardized gamma to which all the positive films are to be developed. A certain raw positive film stock is chosen, and a series of positive films are printed from negatives of different types and developed to difierent gammas and processed into color to determined the lowest positive gamma, for the individual color process used, that will produce a satisfactory black when projected on a theatre screen. This is largely a matter of judgment and may be altered from time to time. The positive gamma should be kept as low as possible, for it is axiomatic that excess development increases grain clumping. By way of example only and using methods described in my patent and patent application cited above, I prefer, with my present knowledge, to develop Kodak "duplitized positive to gammas between .35 and .4, but I do not limit myself to this development. Whatever the gamma selected, it will be hereinafter called the "standard positive gamma.

After the standard positive gamma" is selected, I then determine the standard positive printing time by printing a series of tests from an unexposed negative film that has been developed to produce an average negative emulsion fog. The printer should operate at a fixed speed (preferably driven from a synchronous motor) and be equipped with an accurately controlled light source so exposures can be reproduced accurately. A number of strips of positive film are then printed from the negative film described above, developed to the standardized positive gamma" and either read under a densitometer or projected on a screen to pick out the strip with the least exposure that produced a satisfactory Y black. The minimum positive exposure, printed from a "developed but not exposed negative, that produced a satisfactory black will be hereinafter termed the standard positive printing time.

After the printing light'and gamma of development for the positive film have been determined, a test strip of negative film is exposed in the camera identically with the exposure of the actual scene for which the negative development gamma is to be determined. This strip of film is developed to a series of gamma steps by immersing a few frames (an individual picture on motion picture film) in developer for a fixed time, then a few more frames are immersed in the developer along with the first frames. This action is repeated until a series of steps are developed on the strip varying from apparent under development,

to apparent over development.

In actual practice, using any type of developing machine, I prefer to stop and start the machine at fixed time intervals, and when the minimum time of development is reached (the first steps will receive most development) to run the strip, including the last step, through the developing machine without stopping. For example, if the normal time of development in a given machine is eight minutes and the minimum possible time four minutes, I would prefer to feed a few frames under the developer and stop feeding for fifteen or thirty seconds, then feed a few more frames and stop another fifteen or thirty seconds until the first step had been developed for eight minutes, and then to operate the developing machine at maximum speed for four minutes to produce a test strip with developments varying from four to twelve minutes.

According to my invention, I then print this strip onto a positive film, using the standardized positive printing time" in the printer, and then develop this film to the standard positive gamma and process it into color.

This color print is projected step by step on a screen with standard theatre illumination and preferably. on account of color, with the same source of light in general use in theatre projection. The step producing the best picture, considering the scenes preceding and following it on the screen, is selected and the real scene developed to the gamma of the selected strip.

I prefer to use the same developing machine for both the test and the scene development and to maintain the developer in the machine at as nearly as possible the same strength between the test and scene development.

, If the test strip be developed under different conditions from which the actual scene is to be developed. its gamma must be determined or some means used to insure the development of the actual scene will correspond to test development.

Mechanically an interval timer may be used to start the developing machine motor to feed a few frames into the developer, then stop and repeat the operation at predetermined intervals or the motor may run continuously and a magnetic clutch be used to drive the machine intermittently. The interval timer may consist of a constantly driven commutaton with segments contacting a brush for operating the motor or clutch intermittently. It is also apparent that series of clash gears may be designed for this intermittent operation.

Usually two or three separate films are exposed in modern color separation motion picture cameras. All three films may be test developed in this step by step process, or, for sake of simplicity and time saving, two or even one of the three films may be test developed. If two or three films are o be tested and there is any motion in the test scene, it is important that each of the films be marked in camera so the different films will be in image registry" in all of the test development steps.

Excellent results may be obtained by testing only one of the color separation negative films.

Any one of the three may be used and when.

processed be dyed in any color, for it is not essential that the film be dyed in a color comple mentary to the color of light by which the negative was exposed.

If one negative film only be tested, I prefer to use the red separation negative and to color the positive made from it with the usual cyan dye (blue-green). This color is usually the thinnest and most critical of the three colors in recording the important flesh colors and probably contributes more than any of the other colors to image definition.

Sometimes it is desirable to develop the three separation negatives to different gammas, but these gammas are probably in a mathematical relation to each other; by determining the de sired developing time for the red separation, the timirg for the other developments may be readily calculated.

This method of development control is based on limiting the density of the negative highlights, so the standard positive printing time will just record detail through itand at the same time will print an acceptable black through the clear or practically clear portions of the negative. There is only a certain range of densities possible to the positive process, and this negative control method keeps the negative densities within these limits.

From a technical standpoint I believe that better color film is made by securing the minimum negative densities by exposure and developing to low contrast to control the highlights. It is also my belief that it is diificult in practice on an interior motion picture set to get sufiicient exposure on all three color separation negative films to keep them within the straight line portion of the H and D curve without great exposure for lighting and without the illumination and heat affecting the actors in the scene. With variable gamma development and minimum exposure, the toe" of the H and D curve is not very pronounced and has only a minor affect on the shadows. The benefits from reduced illumination far outweigh its disadvantages, in my opinion, and this negative gamma control system enables it to be used to the fullest advantage.

While the methods herein described constitute the preferred process under this invention, it is to be understood that the invention is not limited to these precise methods, and that changes may be made therein without departing from the scope of the invention,.which is defined in the appended claims.

What is claimed is:

1. A process for determining the development of motion picture negative film, comprising exposing a test strip of film in the camera under conditions identically the same as the scene for which the development is bein determined, immersing succeeding portions of the test strip in developer for varying times to produce a series of steps on the film of varying densities, printing a positive film from this developed test film in a printer for a predetermined standard positive printing time, developing this positive film to'a pre-determined standard positive gamma, selecting a step in the positive test film by inspection and developing the negative of the actual scene in accordance with the development of the negative from which was made the selected step on the positive test film. v

2. A process for determining the development of color separation motion picture negative film,

comprising exposing a test strip of film in the camera under conditions identically the same as the scene for which the development is being determined, feeding the test strip intermittently into developer in a developing machine a few frames at a time to produce a series of steps of decreasing density on the film, printing a positive film from this developed test film in a printer for a pre-determined standard positive printing time, developing this positive film to a pre-determined standard positive gamma and processing it into color, selecting a step in the positive test film by inspection and developing the negative of the actual scene in accordance with the development of the negative from which was made the selected step on the positive test film.

3. A process for determining the development of color separation motion picture negative film, comprising exposing a test strip of film in the camera under conditions identically the same as the scene for which the development is being determined, immersing succeeding portions of the test strip in developer for varying times to produce a series of steps on the film of varying densities, printing a positive film from this developed test film in a printer for a pre-determined standard positive printing time, developing this positive film to a pre-determined standard positive gamma and processing it into color, selecting a step in the positive test that combines good reproduction of the scene as well as harmonizing with other scenes, and developing the negative of the actual scene in accordance with the development of the negative from which was made the selected step on the positive test film.

4. A photographic process comprising selecting a standard gamma for positive pictures, determining the development conditions to produce positives of said gamma, making a negative test strip of a scene to be photographed and developing portions of said test strip to different gammas, developing a positive to the said standard gamma from said test strip, selecting a portion of the positive so produced and developing a final negative of said scene in accordance with the development conditions of that portion of the test strip from which the said selected positive portion was printed and, from the final negative, printingpositives to the said standard gamma.

5. A photographic process comprising selecting a standard gamma for positive pictures, determining the development conditions to produce positives of said gamma, determining a standard least exposure to produce said positives, making a negative test strip of a scene to be photographed, and developing portions of said test strip to different gammas, printing and developing a positive to said standard conditions from a said test strip, selecting a portion of the positive so produced and developing a final negative of said scene in accordance with the development conditions of the portion of the test strip from which the said selected positive portion was printed, and printing and developing a positive to the said standard conditions from the final negative.

PERCY D. BREWSTER. 

